Water spray dental handpieces are conventionally known, with which a dentist may spray water through the tip of the head section of the dental handpiece for cleaning the treatment site or the like. A dental handpiece of this type is known from, for example, JP-3103624-U, and is shown partially in FIGS. 7 and 8 of the attached drawings. The handpiece has a drive section 1 and a handpiece body 3. The drive section 1 has an insert 11 axially projecting in the distal part of the drive section 1, and the handpiece body 3 has an axial bore 30 extending axially and opened in the proximal end face. The drive section 1 is detachably coupled to the handpiece body 3 by inserting the insert 11 into the axial bore 30.
The drive section 1 contains a water line 12a having an outlet aperture 12 opened in the circumferential surface of the insert 11, for transferring water from a water source, and a chip air line 13a having an outlet aperture 13 opened in the circumferential surface of the insert, for transferring chip air from a chip air source.
On the other hand, the handpiece body 3 contains a corresponding water line 301 and a corresponding chip air line 302, both extending to a head section 36 at the distal end of the handpiece body 3. Circumferential grooves 32 and 33 are formed in the inner surface of the handpiece body 3 in the axial bore 30, and communicate with the water and chip air lines 301 and 302, respectively.
When the drive section 1 is connected to the handpiece body 3 by inserting the insert 11 into the axial bore 30, the outlet aperture 12 of the water line 12a in the drive section 1 is brought into communication with the circumferential groove 32 of the handpiece body 3 so that the water lines (12a, 301) in the drive section 1 and the handpiece body 3 are connected. At the same time, the outlet aperture 13 of the chip air line 13a in the drive section 1 is brought into communication with the circumferential groove 33 of the handpiece body 3 so that the chip air lines (13a, 302) in the drive section 1 and the handpiece body 3 are connected.
In this state, water is transferred from the water source through the water lines (12a, 301) to the head section 36, while chip air is transferred from the chip air source through the chip air lines (13a, 302) to the head section 36, where water and chip air is mixed upstream of holes 37, one to four of which are provided in the end face of the head section 36 as shown in FIG. 8 and sprayed through the holes 37.
In a dental handpiece of this type, as discussed above, water and chip air are transferred through the drive section 1 and the handpiece body 3 in separate lines, and mixed in the head section before spraying. It is not possible to switch off the chip air line to stop chip air, while the water line is switched on to allow passage of water only. Thus even if a user of the handpiece wants to use water only depending on the dental procedure, it is not possible to inject only water through the holes 37 in the head section 36 while chip air is stopped.